This invention relates to wireless networks, and in particular, to processing of frame sequences conforming to a wireless medium access control (MAC) protocol.
Wireless networks such as wireless local area networks (WLANs) can be used either to replace wired LANs, or as an extension of the wired LAN infrastructure. IEEE 802.11 is a standard for wireless LANs, and this invention shall be explained with reference to the standard. The invention, however, is also applicable to other wireless networks.
One topology of an 802.11 network is shown in FIG. 1. A Basic Service Set (BSS) includes of two or more wireless nodes, or stations (STAs), which have recognized each other and have established communications. In the most basic form, stations communicate directly with each other on a peer-to-peer level sharing a given cell coverage area. This type of network is often formed on a temporary basis, and is commonly referred to as an ad hoc network, or Independent Basic Service Set (IBSS). In most instances, the BSS contains an Access Point (AP). An access point is a wireless station whose main function is to form a bridge between wireless and wired LANs. The AP also can coordinate communication between the other STAs in the network. The AP is analogous to a base station used in cellular phone networks. An AP can also work as a repeater. When an AP is present, stations do not communicate on a peer-to-peer basis. All communications between stations or between a station and a wired network client go through the AP. AP's are usually not mobile, and form part of the wired network infrastructure. A BSS in this configuration is said to be operating in the infrastructure mode and the network shown in FIG. 1 is such an infrastructure network.
The MAC protocol in the IEEE 802.11 supports two different access methods (“transmission policies”), the mandatory Distributed Coordination Function (DCF) and the optional Point Coordination Function (PCF). PCF provides a polled access mechanism.
Many MAC protocols require a fast response to a received frame. By software implementation of a MAC protocol function is meant the inclusion of a processor in the MAC processing apparatus, and programming instructions (code) for the processor that implement the function. Because of the low latency requirement, a software only MAC implementation requires a fast relatively expensive processor, and possibly complex programming. It is thus desirable to pass on at least some of the MAC functions to hardware, i.e., to include in the MAC processing apparatus some purpose built hardware that performs some of the MAC functions. A complete hardware solution is also possible.
In a combined software/hardware implementation, there is a need to determine how to best divide the functions between hardware and software.
There also is a need to provide MAC processing apparatus that is flexible, i.e., that can accommodate different transmission policies of different MAC protocols, including those not yet invented. The standard DCF and PCF MAC policies may be modified, for example to implement different quality of service (QoS) mechanisms. Such QoS schemes can provide service differentiation between the various priority levels. For example, some real-time applications, such as streaming media that includes real time audiovisual data, may need certain guaranteed QoS. Thus, there is a need for a MAC processor to be easily modifiable to accommodate changes in MAC protocols. A hardware-only MAC is typically very difficult to modify.
Thus, there is a need for a MAC processor that combines hardware elements to implement time critical components, and a processor running software to implement other less-time critical functions. There further is a need to determine what aspects of a protocol to implement in software, and which aspects in hardware.